1. Technical Field
The present disclosure relates generally to a method and system for thermal treatment of tissue, and, more particularly, to a method and system for the hyperthermia treatment of prostatic tissue.
2. Description of Related Art
Benign prostate hyperplasia (BPH) or hyperplasia affects over one out of every two males over the age of fifty. BPH is the non-cancerous enlargement of the prostate gland and is characterized generally by a constriction of the urethra by the prostate gland. An array of symptoms are associated with BPH including frequent urination, complications in urinary flow and associated pain.
Generally there are two primary methods for treating BPH, namely, drug therapy and surgical intervention. Drug therapy incorporates the use of one or more drugs such as Proscar.TM. and Hydrin.TM. to either reduce the size of the prostate or to relax the urethral muscles thereby facilitating the normal functioning of the urinary system. Known drug therapies, however, are limited in their effectiveness and present many drug side effect concerns.
Surgical methods for treating BPH include transurethral resection of the prostate (TURP), transurethral incision of the prostate (TUIP), visual laser assisted prostatectomy (VLAP), balloon dilation and stenting. TURP is the most common method employed for BPH treatment today and involves the insertion of an electrosurgical cutting instrument through the urethral passage. The cutting elements of the instrument are positioned adjacent the prostate gland, and the instrument is energized such that the cutting elements selectively cauterize and resect tissue from the core of the prostate. The TURP procedure, however, has many side effects including bleeding, electrograde ejaculation, impotence, incontinence, edema and a prolonged recovery period for the patient. An example of an electrosurgical cutting instrument utilized in conjunction with a TURP procedure is disclosed in U.S. Pat. No. 5,192,280.
Transurethral incision of the prostate (TUIP) involves the use of an electrocautery device which is passed through the urethra. The device is employed to make multiple incisions in the prostate, thereby permitting the prostate to be displaced from the urethra wall to create an opening for urine flow. Success with the TUIP procedure is generally limited providing only temporary relief and requiring a subsequent repeat of the procedure in the future.
Visual laser assisted prostatectomy (VLAP) includes insertion of a laser catheter through the urethra and directing laser energy laterally through the catheter sleeve at the urethral wall and the prostatic tissue. The laser energy causes the tissue to coagulate. The coagulated tissue eventually necrosis from lack of blood flow and is naturally removed from the body. Drawbacks of VLAP include increased recovery time, acute pain and irritation, and undesired burning of the urethral wall. Examples of methods and apparatuses utilized in VLAP treatment of BPH are disclosed in U.S. Pat. No. 5,242,438 to Saadatmanesh et al. and U.S. Pat. No. 5,322,507 to Costello.
Balloon dilation procedures for BPH involve expanding and stretching the enlarged prostate with a balloon catheter to relieve pressure off the constricted urethra while stenting incorporates the insertion of tiny wire-mesh coils which expand into a scaffold to hold the urethra open. Balloon dilation and stenting, however, are only temporary procedures typically requiring follow up within a year period. In addition, stenting presents complications of stent migration and consequent irritation.
More recently, two new surgical developments, namely, transurethral microwave therapy (TUMT) and high intensity focused ultrasound (HIFU) have been developed for the treatment of BPH. In accordance with a TUMT procedure, a foley-type urethral catheter having a microwave emitting antenna at a probe end is inserted into the urethral passage for a period of time sufficient to treat the tissue by microwave radiation. Intraurethral applicators of this type are described in U.S. Pat. Nos. 4,967,765, 5,234,004 and 5,326,343. The drawbacks of TUMT include the inability to focus the heat energy in the prostatic area and the inability to achieve high temperatures uniformly within the prostate.
High intensity focused ultrasound (HIFU) includes directing high intensity ultrasound waves at the prostate tissue to create heat in a precise area to coagulate and necrose tissue. A transurethral probe is utilized to create the ultrasound beams for both imaging and ablation of the prostatic tissue. Disadvantages of this procedure include the inability to directly focus the ultrasound energy at the prostatic tissue.
A more recent form of treatment for BPH involves thermally treating prostatic tissue with radio frequency electromagnetic energy. For example, one current technique, known as transurethral needle ablation TUNA.TM.), involves the transurethral application of a medical probe having a pair of monopolar RF needle electrodes at its distal end. The probe is inserted into the urethra and advanced to a position adjacent the prostate. Thereafter, the RF needles are advanced to penetrate the urethral wall and access the prostatic tissue. A RF current is transmitted through each electrode and passes through the tissue to a grounding pad to form a necrotic legion which is eventually absorbed by the body. Apparatuses and methods for treating BPH via the TUNA.TM. technique are disclosed for example in U.S. Pat. Nos. 5,366,490; 5,370,675; 5,385,544; 5,409,453; and 5,421,819.
The use of RF electromagnetic energy in the thermal treatment of BPH such as in, e.g., the aforedescribed TUNA.TM. technique, has several limitations. In particular, the use of monopolar RF electrodes presents problems in localizing thermal energy within a desired heating pattern within the prostatic tissue. Moreover, the heating patterns generated by the TUNA procedure with the monopolar electrode arrangement are nonsymmetrical. In addition, the leakage of RF current from the monopolar electrodes to the grounding pad increases the potential of healthy tissue being subjected to thermal energy and destroyed. Furthermore, the monopolar electrode arrangement of the TUNA instrument is limited with respect to its ability to generate heating patterns of various dimensions. Also, monopolar systems require higher frequency applications.
Another significant disadvantage associated with the TUNA.TM. technique concerns the impedance measurements generated with the monopolar electrode and grounding pad arrangement. The electrical impedance of an RF electrode system of a thermal treatment instrument is generally determined during treatment to ascertain the dielectric properties of the treated tissue to thereby provide an indication of the state of the treated tissue and its response to the RF heating pattern. However, with a monopolar electrode system, such as the system utilized in the TUNA.TM. technique, the impedance is dependent upon, in part, the location of the grounding pad relative to the electrode. Thus, a direct measure of the prostatic tissue impedance cannot be ascertained.
Another disadvantages of current RF thermal treatment systems is that these systems are capable of only achieving necrosis of the treated tissue as opposed to complete vaporization. Necrotic tissue entails a two to four week period for complete absorption and natural removal from the body thereby delaying immediate relief of the symptoms of BPH.